If you ask the astronomers of the sharp end of SETI why they think there has been an eerie silence they’ll say, “Well we only have been doing it for 50 years.” “We’ve just started.” “What more do you expect?” “It’s a big universe out there.” And in fact, to put that into context they look carefully. It’s just a few thousand stars. There are 400 billion stars within our Milky Way galaxy alone, so it is a needle in a haystack search.

Well I first suggested the idea in the early 1990s that life could have come from Mars to Earth inside rocks blasted off the Red Planet by comet and asteroid impacts, I think a lot of people felt that this was a pretty crackpot notion. But it became clear during the 1990s that not only is there a large traffic of material exchanged between Mars and Earth, but microbes, if protected by the rock, cocooned inside, could survive the harsh conditions of outer space for a long time - many millions of years.

What if humans made contact with aliens? The chair of the SETI Post-Detection Task Group explains the issues we’d confront and how scientists and government would respond.

Paul Davies

Paul Davies is a theoretical physicist, cosmologist, astrobiologist, and bestselling author. He is Director of the Beyond Center for Fundamental Concepts in Science and co-Director of the Cosmology Initiative, both at Arizona State University. Previously he held academic appointments at the Universities of Cambridge, London and Newcastle upon Tyne in the UK, before moving to Australia in 1990, initially as Professor of Mathematical Physics at The University of Adelaide. Later he helped found the Australian Centre for Astrobiology in Sydney.

Davies’s research focuses on the “big questions” of existence, ranging from the origin of the universe to the origin of life, and include the nature of time, the search for life in the universe, and foundational questions in quantum mechanics. He helped create the theory of quantum fields in curved spacetime, with which he provided explanations for how black holes can radiate energy, and what caused the ripples in the cosmic afterglow of the Big Bang. In astrobiology, he was a forerunner of the theory that life on Earth may have come from Mars. He is currently championing the theory that Earth may host a shadow biosphere of alternative life forms.

Davies has lectured on scientific topics at institutions as diverse as The World Economic Forum, the United Nations, the Commission of the European Union, Google, Windsor Castle, The Vatican and Westminster Abbey, as well as mainstream academic establishments such as The Royal Society, The Smithsonian Institution, and the New York Academy of Sciences. Davies devised and presented a series of 45 minute BBC Radio 3 science documentaries and a one-hour television documentary about his work in astrobiology, entitled "The Cradle of Life." Among his bestselling books are "The Mind of God," "How to Build a Time Machine," and "The Goldilocks Enigma." His latest book, "The Eerie Silence," was published by Houghton Mifflin Harcourt in 2010.